General overview of the temporal bone canals
Temporal bone (os temporale) contains eight independent canals and canaliculi that allow the passage of vessels and nerves between the cranial base, tympanic cavity, and the external surface of the bone. The study of each canal follows a standardized scheme: origin, termination, contents, and course. The name of the canal usually provides a clue about its contents.
The structures under consideration include: the carotid canal, facial canal, musculotubular canal, canaliculus of the chorda tympani, tympanic canaliculus, mastoid canaliculus, caroticotympanic canaliculi, and the canal for the greater petrosal nerve.
Carotid canal and caroticotympanic canaliculi
Carotid canal (canalis caroticus) begins with the external aperture on the inferior surface of the petrous part and ends with the internal aperture at the apex of the petrous part. It contains the internal carotid artery (arteria carotis interna), the carotid venous plexus, and the internal carotid sympathetic plexus. The canal is located near the anterior wall of the tympanic cavity: it first runs vertically upwards, then bends at a right angle and runs horizontally towards the apex of the petrous part.
Caroticotympanic canaliculi (canaliculi caroticotympanici) branch off from the wall of the carotid canal and open into the tympanic cavity. They transmit the caroticotympanic nerves (branches of the internal carotid plexus) and homonymous arteries, which provide innervation and blood supply to the mucosa of the tympanic cavity.
Facial canal and canaliculus of the chorda tympani
Facial canal (canalis nervi facialis) begins at the fundus of the internal acoustic meatus and ends at the stylomastoid foramen. Contents: nervus facialis (cranial nerve VII), geniculate ganglion (ganglion geniculi), as well as the stylomastoid artery and vein.
The course of the canal has two bends. The first turn, located in the horizontal plane, forms the geniculum of the facial canal, where the geniculate ganglion lies. Next, the canal runs posteriorly along the posterior wall of the tympanic cavity, after which it makes a second turn at a right angle and descends vertically downwards to the stylomastoid foramen.
Canaliculus of the chorda tympani (canaliculus chordae tympani) branches off from the facial canal slightly above the stylomastoid foramen and opens into the petrotympanic fissure. It contains the chorda tympani (chorda tympani), a branch of the facial nerve. The nerve passes transit through the tympanic cavity and leaves the bone through the petrotympanic fissure.
Musculotubular canal
Musculotubular canal (canalis musculotubarius) begins with an opening of the same name on the anterior border of the petrous part and opens on the anterior wall of the tympanic cavity. The canal is divided by a bony septum into two semicanals:
- Semicanal for the tensor tympani muscle — contains the musculus tensor tympani;
- Semicanal for the auditory tube — contains the bony part of the tuba auditiva, which continues into its cartilaginous part.
Both semicanals run in parallel and open onto the anterior wall of the tympanic cavity.
Tympanic canaliculus, mastoid canaliculus, and the canal for the greater petrosal nerve
Tympanic canaliculus (canaliculus tympanicus) begins with the petrosal fossa on the inferior surface of the petrous part and ends at the hiatus for the lesser petrosal nerve on the superior surface of the petrous part. It contains the tympanic nerve, a branch of the glossopharyngeal nerve (cranial nerve IX). The nerve ascends to the inferior wall of the tympanic cavity, forms the tympanic plexus there, and then continues as the lesser petrosal nerve, exiting through the hiatus of the same name.
Mastoid canaliculus (canaliculus mastoideus) begins in the jugular fossa and ends at the tympanomastoid fissure. It contains the auricular branch of the vagus nerve (cranial nerve X). Unlike other canals, it does not reach the tympanic cavity.
Canal for the greater petrosal nerve (canalis nervi petrosi majoris) branches off from the facial canal in the region of the geniculum and opens on the superior surface of the petrous part at the hiatus for the greater petrosal nerve. It contains the nervus petrosus major, which branches off from the geniculate ganglion.
Key points
- The temporal bone contains 8 canals; for each, it is necessary to know the origin, termination, contents, and course.
- The carotid canal runs near the anterior wall of the tympanic cavity and contains the internal carotid artery with the sympathetic plexus.
- The facial canal has two bends; the ganglion geniculi is located in the region of the geniculum.
- The musculotubular canal opens onto the anterior wall of the tympanic cavity via two semicanals.
- The canaliculus of the chorda tympani connects the facial canal with the petrotympanic fissure.
- The tympanic canaliculus transmits a branch of cranial nerve IX, which continues as the lesser petrosal nerve.
- The mastoid canaliculus is the only one that does not come into contact with the tympanic cavity; it contains the auricular branch of cranial nerve X.
- The canal for the greater petrosal nerve is a branch of the facial canal originating from the geniculate ganglion.